This invention relates to the production of polymeric carbamates, in particular the continuous production of polymeric carbamates which find use as fuel additives. Such fuel additives, as described in our copending application Ser. No. 801,441, filed May 27, 1977 now U.S. Pat. No. 4,160,648, are highly desirable deposit control additives which effectively limit the deposits in intake systems (carburetor, valves, etc.) without contributing to combustion chamber deposits which cause an increase in the octane requirement of the engine.
Particularly effective additives of this class are monocarbamates produced from polyamines and polymeric chloroformates. By "monocarbamates" is meant carbamates containing a single polyamine moiety linked at an amine nitrogen atom through a carbamate linkage to the oxygen atom of a polyether alcohol. In order to produce substantial amounts of monocarbamate rather than dicarbamate in which two polymeric alcohol moieties are bound to the polyamine at different reactive amine nitrogen atoms, it is necessary to use a large excess of polyamine. Because the reaction between polyamine and polymeric alcohol goes via a polymeric chloroformate intermediate, polyamine hydrochloride is produced in equimolar amount to the desired carbamate. Chloride is untenable in automotive fuels and causes corrosion and plugging of process equipment and should be reduced to very low levels before final separation of the monocarbamate product.
The removal of the hydrochloride salt with recovery of the excess polyamine poses formidable problems. Phase separation between a hydrocarbon phase containing the carbamate product and a polyamine phase containing the hydrochloride salt is a possible procedure. However, the polyamine is in general soluble in the hydrocarbon phase so that the use of large excess polyamine results in a large hydrocarbon phase and a small hydrochloride-containing phase. The hydrochloride-containing phase then forms small droplets distributed through the hydrocarbon phase, fails to agglomerate and/or settles too slowly to allow continuous operation. Washing the product with sufficient water to remove the hydrochloride, or a combination of alcohol and water, has been used in the past, but produces a polyamine-water-polyamine hydrochloride separation problem which is complicated by the large amounts of water present. (If water alone is used in washing, it tends to form an emulsion unless some low-molecular-weight alkanol is also present. This presents further separational complexity.) The complete removal of chloride ion from the product is required for efficient separation of the product carbamate by distillation and the use of the carbamate in gasoline fuels. A stringent upper limit of about 10 ppm or less of chloride ion is specified for the hydrocarbon phase containing the carbamate.